Four wheel steer allows all four wheels of a motor vehicle to contribute to the steerability of the vehicle. At low speeds, the rear wheels turn in the opposite direction of the front wheels to improve maneuverability by minimizing the turn radius. At higher speeds, the rear wheels turn in the same direction as the front wheels to increase vehicle stability. Both situations provide particular advantages for long wheelbase vehicles such as full-size trucks, vans, and sport utility vehicles which could benefit from improved maneuverability and stability.
To accomplish four wheel steer, the vehicle wheel track width may increase to accommodate additional steering components such as knuckles, yokes, and ball joints. Extending the wheel track width increases the overall mass of the vehicle. A further consideration for large vehicles is Federal Motor Vehicle Safety Standard 108 which requires two clearance lights on vehicles over 80 inches wide. Therefore it is desirable to manage the additional lateral packaging space required to accommodate four wheel steer.